<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script src="js/vue.js"></script>
</head>
<!-- 
   
       vm.$watch('isHot', {
            immediate: true, //初始化是让handle调用一下
            handler什么时候调用当isHot发生改变时
            handler(newValue, oldValue) {
                console.log('isHot被修改了', newValue, oldValue);

            }
        })
       
 -->

<body>
    <div id="root">
        <h2>今天天气很{{isHot?'炎热':'凉爽'}}</h2>

        <button @click="isHot=!isHot">切换天气</button>
    </div>
    <script>
        Vue.config.productionTip = false;

        const vm = new Vue({
            el: "#root",
            data: {
                isHot: true
            },
            computed: {
                info() {
                    return this.isHot ? '炎热' : '凉爽'
                }
            },
            methods: {
                changeWeather() {
                    this.isHot = !this.isHot;
                },

            }
        })
    </script>
</body>

</html>